EP-A-0 612 818 describes cathodic electrodeposition lacquers which comprise, in addition to an acid-neutralized CEL binder, crosslinked polymer microparticles which have been prepared by mixing an acrylic polymer with tertiary amine functions and a polyepoxide, dispersing the mixture in an aqueous medium and heating the dispersion for the purpose of crosslinking.
Cathodic electrodeposition lacquering is an industrial process which is susceptible to impurities, which manifest themselves adversely during stoving of the cathodically electrodeposited coats of lacquer as surface defects, for example as craters. The impurities here can originate from the lacquer bath or from the ambient air. Since it is practically impossible to eliminate from the CEL process the impurities which are responsible for the adverse surface phenomena and are often already harmful in traces, the remedy in the past has been addition of additives to the CEL baths. Although the additives help against the undesirable surface defects, they often interfere with the adhesion of coats of lacquer subsequently applied, especially at a higher dosage.